Protective coatings for articles



Patented Jan. 2, 1945 PROTECTIVE COATINGS FOR ARTICLES Gunnar Lindh, Detroit, Mich assignor to The Udylite Corporation, Detroit, Mich a corporation 01' Delaware No Drawing. Application May 29, 1942, Serial No. 445,011

Claims.

This invention relates to protective coatings for articles and more particularly to protective coatings for'articles useful in performing chemical, processes such as liquid chemical dips, elecfor polymethacrylat coatings without afiecting adversely the chemical resistance offered by them.

The amount of vinylidene chloride-vinyl chlotrochemical cleaning, electroplating, chemical 5 rid Ki-P l r is l mi d t a ou 2 0f th oxidation, phosphatizing, chromatizing, etc. total resin content because larger amounts cause Machines and parts thereof used in chemical the coating to lose some of its adhesion and treatment are corroded or otherwise afiected by ons er b e of s es making t generthe chemical treatment. For example, work ally unsu t b r co s o et a t c holding racks and tanks for the electrolytes used I am familiar with the fact that vinylidene in electrodeposition of metal ar corroded by chloride and esters of methacrylic acids have reacting with the electrolytes and metal is debeen co-polymerized in reaction kettles to proposited on the racks and tanks. It is the object vide a resinous composition, subsequently disof this invention to produce a protective coating solved in solvents as shown in United States for such machines and machine parts which will Patents Nos. 2,160,945, 2,249,915, 2,249,916 and eiifectively protect the same against reactive contact with the chemicals, either gaseous or liq- My material diflers from these in that I do uid, used in well-known chemical treating procnot co-polymerize the methacrylic acid ester with esses. the vinylidene chloride but use a mixture of This object has been achieved by coating the already polymerizedmethacrylic acid ester and machine or machine parts with a iprotectivefilm already co-polymerized vinylidene chloride and comprising a mixture of a polymethacrylic acid vinyl chloride. ester and a co-polymer of vinylidene chloride There is no precise lower limit to the amount and vinyl chloride. Y of the vinylidene chloride-vinyl chloride co- It is the purpose of this invention to provide polymer. Naturally, when a. very small amount coatings of great hardness and wear resistance is added, the plasticizing eifect is small. Though combined with considerable flexibility and havsome effect may be noted with as littl as 1%, ing a high chemical resistance, especially to such for my purposes I prefer to use at least 5% and solutions as are used in the plating art. generally about 15-20%.

Thi invention also contemplates a coating Polymethacrylates are soluble in inexpensive having good adhesion to metal. solvents such as toluol, xylol and esters such as Very hard and adherent coatings are proethyl-, butyland amyl acetates. My plastiduced with polymethacrylates alone and especizer, however, is insoluble in the aromatic naphcially with polymethyl methacrylate, particuthas and only slightly soluble in the esters. It larly when the coatings are subjected to heat, is soluble in ketone type solvents such as acefor example, for 20 minutes at 300 F. or one tone, methyl ethyl ketone, methyl isobutyl ketone hour at 250 F. However, such coatings tend to and cyclohexanone, ethers such as dloxane and be brittle and cannot be used for many puriso-propyl ether and chlorinated ethylene composes. The need for a plasticizer is indicated. pounds such as ethylene dichloride. Hence, it The common commercial plasticizers such as is desirable to add ketones, ethers or chlorinated dibutyl phthalate and tricresyl phosphate, when ethylene compounds to the solvents when my added to the methacrylate, does remove the explasticizer is employed. I have also found that treme brittleness of the baked resin coating. while Saran B is not completely soluble in nitro- However, they also adversely affect the chemiparaflins, these solvents, for example, 1- or 2- cal resistance of the coating. nitro-propane, can be used with other solvents I have found that co-polymers of vinylidene when coatings containing relatively small chloride and vinyl chloride, such as manufacamounts of Saran B are employed. tured by Th Dow Chemical Company under the The following combinations have proven very trade name "Saran B, are excellent plasticizers satisfactory:

solids mmmsiflom Solvent composition, per cent byweight Total solids, per cent by weight so n t s zl gltt per cent M hl 1 1" 153m samnB weight Toluol x7101 a ce at tt a i' t a t eethyl tre t ono pt p ge g 33 it 33 $3 12 1? 3 a1 80 g g 5; 12 4 3 $3 22 62 13:33:: "2s 1o In coating a rack tor electrochemical processing and the like, I proceed as follows: The coating solution is kept in a container and the rack is lowered into it suillciently slowly that air be not entrapped with the coating. The rack is then withdrawn at a low rate of speed, approximately /2 in. to 1 in. per minute. Any drops of coating material adhering to the lower end are easily wiped oil with a stick, and the coating re-forms rapidly over this area because of its high surface tension. The rack is now allowed to air dry for about one hour or force dry, for example, at 225 F., for twenty minutes.

Subsequent coatings are then applied in the same manner until the required total thickness is obtained. Every other coating application is made with the rack turned upside-down to equalize the distribution of the coating. Six coatings are suflicient for most ordinary purposes. For best results, force drying at a temperature of about ZOO-225 F. for about two hours or more is employed after the final coating has been applied.

As the solvents are evaporated, the hardness and adherence increase to maximum. No further increase in hardness takes place because of oxidation, and the coating stays flexible and does not crack during use.

Tanks and similar containers which on account of their size, cannot be dipped, are best coated by spraying. A thin coating is applied at a time and dries sufficiently quickly so that when the whole object has been given one coat, it is usually ready for another coating.

These coatings have shown an unusual and unexpected resistance to the action of chemicals used in the plating art. Thus, for example, coatings of my material thick withstood immersion in a standard chromium plating solution containing 33 oz. per gal. of chromic acid and .33 oz. per gal. of sulphuric acid, operated at a temperature of 110 F. continuously for twentyfour hours without showing any evidence of attack or change of any sort. The same coating was immersed for the same length of time in an alkaline cleaning solution containing about 12 oz. per gal. of a mixture of sodium phosphates, sodium silicates and caustic soda at 210 F. without showing any change in properties. coatings heretofore used, applied in the same thicknesses, were definitely inferior in some respect or another. Thus, for example, a coating consisting of a co-polymer of vinyl chloride,

styrene and vinyl acetate completely lost adhesion in the above-mentioned alkaline cleaner test.

A co-polymer of vinyl chloride and vinyl acetate lost much adhesion and became embrittled during the same test. Other commonly used rack coatings of unknown composition corroded rapidly in the alkaline clean'er. Cellulose and rubber coatings which I tried wer rapidly attacked by the chromic acid bath, being dissolved in the bath and causing a reduction of hexavalent chromium to trivalent chromium.

My coating has also been used in other solutions such as cyanide plating solutions and bright nickel plating solutions as well as acid pickling solutions. A remarkable chemical resistanc and Other absence of hardening and cracking has been demonstrated. No change inadhesion has been noticed.

Compared to the coatings described in my copending application Serial No. 441,478 and comprising mixtures of vinylidene chloride-vinyl chloride co-polymers and finely divided silicious material, my present coating is much harder and has a somewhat less perfect adhesion. By the addition of finely divided silicious material, the adhesion of my present coating can be increased further.

I claim:

1. An article adapted for use in performing a chemical process having a hard protective coating of high chemical resistance, good adhesion and wear resistance, comprising essentially a mixture of polymethacrylic acid ester and a copolymer of vinylidene chloride and vinyl chloride, the said co-polymer of vinylidene chloride and vinyl chloride being present in said mixture in an amount falling within a range of from about one percent (1%) to about twenty-five percent (25%) of the total resin content.

2. An article adapted for use in performing a chemical process having a, hard protective coating of high chemical resistance, good adhesion and wear resistance, comprising essentially a mixture of polymethacrylic acid ester and a copolymer of vinylidene chloride and vinyl chloride, the said co-polymer of vinylidene chloride and vinyl chloride being present in said mixture in an amount falling within a range of from five percent (5%) to twenty percent (20%) by weight of the total resin content.

3. An article adapted for use in performing a chemical process having a hard protective coating of high chemical resistance, good adhesion and wear resistance, comprising essentially a mixture of polymethyl-methacrylate and a copolymer of vinylidene chloride and vinyl chloride, the said co-polymer of vinylidene chloride and vinyl chloride being present in said mixture in an amount falling within a range of from about one percent (1%) to about twenty-five percent (25%) of the total resin content.

4. An article adapted for use in performing a chemical process having a hard protective coating of high chemical resistance, good adhesion and wear resistance, comprising essentially av mixture of polymethyl-methacrylate and a copolymer of vinylidene chloride and vinyl chloride, the said co-polymer of vinylidene chloride and vinyl chloride being present in said mixture in an amount falling within a range of from five percent (5%) to twenty percent (20%) by weight of the total resin content.

5. A coating solution comprising essentially a mixture of polymethacrylic acid ester and a copolymer of vinylidene chloride and vinyl chloride, the said co-polymer being present in said mixture in an amount falling within a range of from about one percent 1%) to about twentyfive percent (25%) of the total resin content, a solvent for the ester and a solvent for the said co-polymer.

GUNNAR LINDH. 

